temp diffusion temperature in
°Ctime diffusion time in
mindop type of the dopant,
select Boron or Phosphorus

Notes

The ability of silicon dioxide to act as a dopant mask in high temperature
diffusion is widely used in MEMS device fabrication. The diffusivity of
dopants like Boron and Phosphorus is much smaller in silicon dioxide compared
to silicon. So silicon dioxide is widely used as a mask to selectively protect
areas of silicon that require no doping.

This design interface can be used to calculate the oxide thickness required to
mask the high temperature pre-deposition of either Boron or Phosphorus for a
given time and temperature. Phosphorous diffuses faster through silicon
dioxide and hence a thicker layer of oxide is required to mask Phosphorus.
Arsenic diffuses slower than Phosphorus and hence a mask suitable for
Phosphorus diffusion will be effective against Arsenic

The plot shows the oxide mask thickness over diffusion time in a log-log plot.
This plot is for the selected temperature and the selected dopant.
Using the crosshair, the mask thickness for any diffusion time can be found
out.

Assumptions

-Doping is in the absence of hydrogen, fluorine or other impurities..-The
dopants diffuse uniformly through the oxide.-The concentration of the dopant
on the surface of the oxide is constant.-The source of the dopant is vapor
based with an ambient nitrogen atmosphere.